Carbing and Nitrogen

How are you guys carbing you beer, when you're using nitrogen for you keg beer? Priming sugar in the keg? Force Carb with CO2, then purge and attach the nitrogen (if doing this method should I use straight nitrogen or 75% nitrogen/25%co2)?

I prime with a straight co2 tank first. ASAIK no one uses straight nitrogen. The point of the beer gas it to be able to use a higher pressure to force the beer through a restrictor plate which then knocks most of the co2 out creating a cascading effect. This effect of course gives you that nice creamy head and tiny bubbles.

So anyway I figure out the pressure I would need to carbonate my beer at for the volumes of CO2 I want.

For example: my keggorator is set to 40 degrees and I want 2 volumes of CO2 in my finished beer. I then set my pure CO2 tank to 6 psi and let it carb up over 2 weeks or so. Then I want to switch it to beer gas. This is where it gets tricky. You need to know the mix you have. I have 30% CO2 and 70%N I believe this is typical. Nitrogen will not absorb into the beer but CO2 will. In order to keep 2 volumes of CO2 in your beer you have to keep the equivalent of 6 psi of 100% CO2 in the tank. Because my beer gas is about a third CO2 I simply multiply my original 100% CO2 PSI by 3.33. So in this case I would set my beer gas tank to about 20 psi. This should keep the same level of carbonation and allow the beer gas to do its restrictor plate magic.

If your blend is 75%N 25% CO2 then you are multiplying your first number by 4. 80%N 20%CO2 multiply by 5 ect.

The term "Carbonation" refers to Carbon Dioxide gas being dissolved into a liquid. For this reason we are unable to carbonate with Nitrogen. Ni will not dissolve in liquid like Co2 at the temperatures and pressures we work at.

This is one reasons the mix is used by the Europeans, it can push the beer for the kegs/casks in the back of the pub/bar to the front where the taps are at relatively low pressures and without additional Co2 being added to their beer.

Cheers..